The Burakumin of Japan, the Paekchong of Korea, and
the Cagots of France … What do they have in common? All three were despised
castes—closed groups of people who married among themselves. A despised caste
is not just a low class. Otherwise, it would always be gaining and losing
members, with some moving up and out and others down and in. As Gregory Clark
has shown, the English lower class is descended largely from people who were
middle or even upper class a few centuries before. This may seem strange if you equate the middle class with voluntary childlessness, but until the late
19th century they were the ones who had the most children—even more so if we
look only at children who lived to adulthood. The resulting demographic
overflow continually spilled over into the lower class.

In contrast, not much new blood flows into a
despised caste, at least not on an ongoing basis. Social stigma discourages
people from marrying out or marrying in. Nor does one enter simply by virtue of
being poor, since the fear of losing caste keeps out most of the downwardly
mobile. Despite this lack of new blood, a despised caste can perpetuate itself
indefinitely because its members usually have enough resources—through their
monopoly over equally despised occupations—to get married, form families, and
have enough children to replace themselves. This was not the case with urban
lower classes of pre-industrial times, which typically had large numbers of
childless single men.

Because a caste is closed and self-perpetuating, it may
preserve genetic traits that disappear everywhere else. It thus becomes more
and more different not because it is changing but because its host population
is changing.

But how can a population change over a few
centuries? Didn’t human nature assume its present form back in the Pleistocene
when cultural evolution took over from genetic evolution? In reality, these two
evolutionary processes have reinforced each other. Human genetic evolution
actually accelerated 40,000 years ago and even more so 10,000 years ago,
apparently in response to a growing diversity of cultural environments.

What about Richard Lewontin’s finding that human
genes vary much more within populations than between populations? Isn’t that
proof that genetic evolution stagnated while humans were spreading over the
earth and forming the many populations we see today? Lewontin’s finding is
correct but does not mean what it seems to mean. Indeed, the same genetic overlap has
been found between many species that
are nonetheless distinct anatomically, morphologically, and behaviorally.
Genetic variation between populations differs qualitatively from genetic
variation within populations. In the first case, genes vary across a boundary
that separates different environments and, thus, different selection pressures.
This kind of genetic variation is shaped by selection and gives rise to real
phenotypic differences. The situation is something else entirely when genes
vary among individuals who belong to the same population and face similar selection
pressures. That kind of variation matters much less, the actual phenotypic
differences often being trivial or nonexistent.

Human evolution is a logarithmic curve where most of
the interesting changes have happened since the advent of farming and complex
societies. Homo sapiens
was not a culmination but rather a beginning … of gene-culture co-evolution. There
are many ways to study this co-evolution, but one way is to look at the
different evolutionary trajectories followed by castes and their host
populations.

I look forward to reading this. As others have pointed out, all I'm getting is the jpeg of the cover.And I'd also like to hear your views on the largest of such marginalised groups, the Dalits of India.

not much new blood flows into a despised caste, at least not on an ongoing basis...One of the few ways 'new blood' flows into a despised caste is when an upper caste guy decides to fool around with his cleaning girl. That happens quite a lot, sometimes with and sometimes against her wishes. Young, attractive despised caste girls have always been perceived as morally lax and fair game.

"Genetic variation between populations differs qualitatively from genetic variation within populations. In the first case, genes vary across a boundary that separates different environments and, thus, different selection pressures. This kind of genetic variation is shaped by selection and gives rise to real phenotypic differences. The situation is something else entirely when genes vary among individuals who belong to the same population and face similar selection pressures. That kind of variation matters much less, the actual phenotypic differences often being trivial or nonexistent." I don't see where you have cited anyone for that idea?

On the other hand, citing obscure anonymous bloggers like Jayman is a real mistake. But that's just my opinion. By the way, I like the reader, it's restful on the eyes and makes it easier to concentrate.

"In the first case, genes vary across a boundary that separates different environments and, thus, different selection pressures. This kind of genetic variation is shaped by selection and gives rise to real phenotypic differences. The situation is something else entirely when genes vary among individuals who belong to the same population and face similar selection pressures. That kind of variation matters much less, the actual phenotypic differences often being trivial or nonexistent."

That's partly begging the question. First, "qualitative" here is nothing but a reiteration of "adaptive", which is a less vague description to what the difference actually is, and yet, it's not all the difference between different environments that is adaptive/"qualitative", due to genetic drift and founder effects. And finally, "qualitative", being really just "partly adaptive" is relative to the environment, therefore "trivial" phenotypic differences within a given environment may be the ones selected for or against in another, and yet they remain exactly the same, only differing in relative frequencies.

Additionally, when we're flirting with explanations of behavioral differences, it's really important not to forget that the main organ responsible for behavior is almost by its very definition an adaptation to confer malleability of behavior, adapting it non-genetically to different situations and environments. And when we're thinking of human behavior specifically, life-history, culture, and economy, will generally suffice for the most parsimonious explanations, with a reduced role for genetics. Twin studies can be misleading here as it compares entire clonal phenotypes and conflates clonal genetic copies with an imprecise notion of "genetic similarity", when "shuffling" the same genes with the rest of the populational genetic variation will weaken the effect of each single gene on the final phenotype. Popular expositions of the subject will also focus on the most curious cases, in a way that's reminiscent of the stories about the coincidences between the two Laura Buxtons, while neglecting differences that may be just as astounding for the stereotypes of twins.

Welcome to my blog! For the most part, this page will be an extension of my website, with comments relating to my research. But it will also branch out into more general discussions of human evolution.